The present invention is concerned with an etchant composition and especially with a composition that is capable of removing inorganic polymer residue present on a substrate due to a previous metal reactive ion etching process. In addition, the present invention is directed to a method for removing such polymer residue by employing the etchant compositions of the present invention.
Aluminum and aluminum alloys are frequently used for the xe2x80x9cmetallizationsxe2x80x9d in large scale integrated circuits. The aluminum alloys include those with small amounts of copper for reducing the potential for electromigration effects, where current applied to the device induces transport of the aluminum atoms. Small amounts of silicon or titanium have been added to aluminum in order to minimize the possibility of electrical spiking that can occur in contact holes.
In order to form the patterned metallization, a series of process steps are carried out. These include depositing a layer containing aluminum, coating a photoresist film onto the aluminum containing layer, creating in the photoresist film an image of the predetermined required pattern, such as by exposing selected portions of the photoresist film to light passing through a mask or grating, and then removing either the exposed or unexposed portions of the photoresist film, depending upon the type of resist employed, and finally removing the aluminum or aluminum alloy layer in the regions not masked by the remaining photoresist film. Next, the remaining photoresist film can be removed.
More particularly, aluminum/copper metal line for BEOL wiring/interconnect in semiconductor devices are currently delineated by a reactive ion etching process. Such a process involves patterning the aluminum/copper metal layer with a photoresist and then reactive ion etching (RIE) in a chlorine environment using boron trichloride, HCl gas, Cl2 or any other chlorine containing reactive species in order to etch away the exposed aluminum/copper layer. However, such etching process leaves a residue around the metal lines which consist of complex polymeric oxides of aluminum along with incorporating chlorine into the inorganic matrix. This is typically referred to as sidewall polymer residue, and its presence is a troublesome source of corrosion of the Al/Cu lines when exposed to the environment such as atmospheric air and/or humidity. Moreover, trace amounts of chlorine over time break down the passivating layer of aluminum oxide and corrode the underlying aluminum. Traditionally, the use of fluoride containing compounds in general, and hydrofluoric acid in particular, has been avoided because it has the tendency to degrade the quality of metal lines in general, and aluminum in particular.
Additionally, after a RIE process, sidewall polymers remain on the semiconductor wafer surface. These sidewall polymers, known as xe2x80x9cpolymer railsxe2x80x9d are inorganic in nature and have various chemical constituents, including aluminum, silicon, titanium, oxygen, carbon and chlorine. Since each of there constituents tend to react and/or interfere with the semiconductor wafer function, removal of the sidewall polymers is therefore desirable. A post metal RIE cleaning step is presently done using a chromic/phosphoric acid etch, or solvent based chemistry methods. However, one common chemical constituent with a solvent based chemistry is an amine which can cause problems with certain types of photoresists. Solutions which are based on diluted sulfuric acid and hydrogen peroxide mixtures have been introduced in an attempt to remove polymer rails. However, these methods have not been successful in removing all types of polymer rails. For example, as shown in FIG. 1, in regions where there is an isolated metal pad which has a metal line density lower than the array region of the semiconductor chip and a surrounding region which is predominantly silicon oxide, current methods are less than completely successful. FIG. 1 illustrates a situation where the use solution of the present invention would be indicated. In FIG. 1, a wafer is shown after it has undergone a RIE process. The direction of the RIE process is shown by the arrow. The structure shown, 10, can be comprised of multiple layers. For example, there can be an oxide layer, 11, and a conductive layer, 12. The RIE process selectively removed portions of the conductive layer to expose the oxide layer. Accordingly, there is little to no residual left on the surface, 5, of the oxide, 11. The RIE process was, in this case, directed at the surface, 5, as shown by the arrow. However, the structure, 10, may contain a solid film, 15, covering the sidewalls, 13 and the top, 14, of the structure, 10.
Alternatively, as shown in FIG. 2, the etchant is useful for processing steps not involving polymer etching. For example, there could be regions in an oxide layer, where a via, 25, has been previously formed and filled. Preferably the material filling the via, 25, would be a conductive material. The via may provide electrical communication between different levels of the wafer. The etchant solution of the instant invention would also be useful for cleaning the via, 20, which is opened to the via, 25, of many types of residue material. Residue materials include, but are not limited to oxygen, silicon, carbon and elements of an underlying conductive layer.
Accordingly, methods are suggested for removing this sidewall polymer residue and polymer rails. One of the more popular method employs a chromic/phosphoric acid bath. However, this procedure is only marginally effective. Moreover, the chromic/phosphoric acid bath tends to cause some electrochemical etching of aluminum, especially near tungsten studs, which are typically present, thereby causing degradation of the aluminum metal layer.
Accordingly, providing an etching process capable of removing the sidewall polymer and via residue that does not etch conductive materials, especially aluminum, to any undesired extent, while removing the sidewall polymer residue would be desirable.